Emission standards for unburned hydrocarbons, carbon monoxide and nitrogen oxide contaminants continue to become more stringent. In order to meet such standards, catalytic converters containing a three-way conversion (TWC) catalyst are located in the exhaust gas line of internal combustion engines. Such catalysts promote the oxidation by oxygen in the exhaust gas stream of unburned hydrocarbons and carbon monoxide as well as the reduction of nitrogen oxides to nitrogen.
Layered catalysts can offer conversion functionality upon careful design of the materials of each layer. Ensuring that the materials are physically available (for example, not sintered or agglomerated) and active to convert exhaust gas throughout the life of the catalyst is an on-going goal.
There is a continuing need to provide a TWC catalyst that provides sufficient conversion so that stringent HC, NOx, and CO emission limits can be achieved cost-effectively.